1. Field Of The Invention
The present invention relates to an apparatus for processing embroidery data necessary for a sewing machine to form an embroidery in an area by filling the embroidery area with stitches.
2. Related Art Statement
There is known an embroidery data processing device of a type which has (a) block data storing means and (b) stitch position data producing means. The block data storing means stores sets of block data each representative of a corresponding one of elementary blocks in an embroidery area for an embroidery such as letters, numerics, and symbols, which blocks are arranged in an embroidering direction in which the filling of each block with stitches is advanced. The stitch position data producing means produces, by utilizing the block data stored in the storing means and, in addition, data indicative of a stitch density selected by an operator, sets of stitch position data indicative of respective stitch positions at which a sewing needle pierces a workfabric to form the stitches.
Generally, an elementary block is defined or enclosed by four line segments. In other words, the outline of an elementary block consists of four line segments. Blocks are classified into two types, one of which is a quadrangular type whose outline consists of straight line segments and the other of which is a curvilinear type whose outline consists of line segments including at least one curved line segment. Regarding an embroidery area illustrated in FIG. 11, a quadrangular block approximates a part of the embroidery area which part is defined by, and between, two curved line segments each belonging to the outline of the area. More specifically described, a pair of opposite sides of the quadrangular block approximate corresponding curved line segments of the outline, respectively. In the meantime, regarding an embroidery area of FIG. 12, a curvilinear block is defined by, and between, two curved line segments each belonging to the outline of the embroidery area, that is, the curvilinear block has the two curved line segments as a pair of opposed line segments thereof. The curvilinear block represents with fidelity a part of the area which part is defined between the two curved line segments.
Generally, block data representative of a quadrangular block consists of sets of position data each indicative of the position of a corresponding one of vertices of the block.
The embroidery data processing device of the above indicated type is adapted to store block data for quadrangular blocks. Therefore, a great number of rectilinear blocks, or, division base points as vertices of those blocks are needed for accurately approximating the outline. Consequently, the block data storing means of the device is required to have a large storage capacity.
The above device suffers from another problem. For storing block data for quadrangular blocks arranged in an embroidering direction in an embroidery area, it is required to divide each of two portions of the outline which portions are opposed to each other generally in a direction perpendicular to the embroidering direction, into the same number of straight line segments which cooperate with each other to approximate a corresponding one of the opposed portions of the outline. The embroidery area is filled with stitches formed by alternately connecting with thread between the opposed portions in the embroidering direction, so that an embroidery is produced in the area. However, the degree of approximation for one of the opposed portions of the outline will be more or less different from that for the other portion, and therefore an excessively high degree of approximation will be given for one of the opposed portions of the outline. For this reason, too, the block data storing means of the device needs a great storage capacity. This problem will be described in more detail by reference to examples illustrated in FIGS. 13 and 14, in which a letter "O" is embroidered on a workfabric.
FIGS. 13 and 14 each show the same part of letter "O", which part includes two curved line portions belonging to an inner and an outer closed line, respectively, which lines constitute the outline of the letter. As described above, for dividing letter "O" into quadrangular blocks, it is required to divide each of the inner and outer closed lines into the same number of straight line segments which approximates a corresponding one of the two closed lines. However, in such a case, the degree of approximation for one of the inner and outer closed lines will be different from that for the other closed line. In the meantime, if each of the two closed lines is divided into straight line segments of the same length for the purpose of giving substantially the same degree of approximation for the each closed line, the number of the straight line segments for the outer closed line will be greater than that for the inner closed line, because an overall length of the outer closed line is longer than that of the inner closed line. Consequently, some of the points determined on the outer closed line for the purpose of dividing letter "O" do not find corresponding points on the inner closed line. The quadrangular blocks obtained in this way suffer from inappropriate profiles or shapes largely deviated from ideal, quadrangular shapes in which stitches are advantageously formed with uniform stitch density. Thus, it is difficult to divide letter "O" into quadrangular blocks while simultaneously giving the same degree of approximation for each of the outer and inner closed lines.
As is apparent, from the foregoing, for dividing letter "O" into quadrangular blocks, it is required to divide each of the inner and outer closed lines into the same number of straight line segments, by sacrificing the requirement of giving the same degree of approximation for each closed line. In this case, the inner closed line is divided into straight line segments of excessively short lengths, namely, excessively high approximation degrees, as shown in FIG. 14.
In short, in the event that the above indicated processing device stores block data for letter "O", it is required to divide each of the outer and inner closed lines of the outline into the same number of straight line segments, although such division is not needed for achieving the purpose of giving the same degree of approximation for each closed line. Consequently, an excessively large number of blocks are derived from letter "O", and therefore the storing means is required to have an excessively large storage capacity capable of storing block data for such a large number of blocks.
There is known another embroidery data processing device capable of transforming the figure of outline of an embroidery or embroidery area. The transformation is, for example, magnification, contraction, or rotation. The processing device includes (1) block data storing means for storing block data (hereinafter, referred to as original block data) which represent quadrangular blocks in an embroidery area, for example, in normal size, (2) modifying means for modifying the original block data and thereby transforming the quadrangular blocks, and (3) producing means for producing, by utilizing the modified block data representing the transformed quadrangular blocks, embroidery data necessary to fill with stitches each of the transformed blocks.
In the event that the modifying means of the above indicated, second processing device modifies original block data for quadrangular blocks approximating a part of an embroidery area which part is defined by, and between, two curved line portions of the outline which portions are opposed to each other on the outline, straight line segments (sides of the quadrangular blocks) approximating the curved line portions are subjected to transformation such as magnification. If the original block data is so modified as to magnify the quadrangular blocks by a ratio or rate selected by an operator, the modified block data result in forming an embroidery which suffers from undesirable burrs or indentations along the magnified outline. As the rate of magnification is increased, the amount of offset between the curved line segments and the straight line segments approximating the curved line segments, is increased. It will eventually be recognized by the naked eye that the outline of the embroidery is approximated by the straight line segments.